[unreadable] This proposal focuses on the development of drug-responsive protein regulatory domains through the computational redesign of nuclear hormone receptors (NHRs). Members of this large family of ligand dependent transcription factors activate transcription upon binding to the appropriate hormone through a C-terminal ligand-binding domain (LBD). In their unliganded states, many of these receptors are bound and inactivated by a multi-component chaperone complex that specifically recognizes the apo form of the LBD. As a consequence, this domain can be fused to non-receptor proteins to confer hormone-dependence to their activities. Hormone-responsive regulatory systems of this type are already having a significant impact on biomedical research, though they suffer from a lack of orthogonality to wild type hormone/receptor signalling networks. We propose to drastically redesign the LBD from a member of the NHR superfamily (the human estrogen receptor) using computational methods developed and validated in the Hellinga lab. by designing domains to respond to non-natural small molecules, we postulate that it will be possible to develop fully orthogonal synthetic genetic regulatory elements for a variety of research and clinical applications. [unreadable] [unreadable]